Vortex flowmeters are used in the industrial process control field for measuring a flow rate of a fluid. Vortex flowmeters are typically inserted in a flow pipe or conduit that carries the fluid to be measured. Industry applications include petroleum, chemical, pulp and paper, mining and materials, oil and gas. The operating principal of a vortex flowmeter is based on a phenomenon of vortex shedding known as the von Karman effect. As fluid passes a bluff body, it separates and generates small eddies or vortices that are shed alternately along and behind each side of the bluff body. These vortices cause areas of fluctuating pressure that are detected by a sensor. While the frequency of vortex generation is essentially proportional to fluid velocity, this proportionality varies with the conduit Reynolds number. The conduit Reynolds number is a function of the fluid density, the fluid viscosity, the fluid velocity, and the inside diameter of the conduit.
In piping systems, there is a desire to keep the Reynolds number low in order to reduce power loss in the piping system. This desire to reduce power loss leads to use of larger pipe sizes and lower ranges of fluid flow velocity in the piping system.
In vortex flowmeters, there are limits to the range of flows that are measurable. When flow velocities are below a lower limit of measurable flow, the vortex flowmeter cannot be relied upon to provide an accurate indication of flow.
There is a need to provide a vortex flowmeter with an accurate flow output over a range of flows found in piping systems where a larger pipe size is used to reduce power loss.